Nerve endings in the skin layers are particularly sensitive to medical treatments that interact with the patient's skin. These types of medical treatments include, for example, hypodermic injections and skin ablation, especially using powerful laser ablation devices. No matter how necessary the medical treatment, the associated levels of pain can be great enough to not only cause patient discomfort, but to mandate that pain relief in some form be provided. It is of course preferable to avoid using pain relieving drugs such as Novocaine, whenever possible. Accordingly, different types of pain relieving devices have been explored. Cooling of the skin has been observed to lessen pain associated with hypodermic injections. As reported in a JAMA research letter entitled “Pain Associated with Injection Using Frozen Versus Room-Temperature Needles,” K. Denkler, Oct. 3, 2001, the use of ice-cold needles have been found to minimize injection pain in procedures that require several needle sticks for each area to be treated.
The cooling of a patient's skin to lessen the pain of hypodermic injections is also described in several U.S. patents. For example, U.S. Pat. No. 4,725,265—Sairenji places a cooling gas injection nozzle adjacent a syringe-mounted hypodermic needle. In addition to the cooling gas injection nozzle, a source of cooling gas in the form of a cooling gas cylinder may be mounted to the barrel of the hypodermic syringe. Accordingly, two external assemblies are required to be secured to the outside of the syringe barrel, thus rendering the syringe assembly cumbersome and difficult to operate.
U.S. Pat. No. 5,236,419—Seney discloses a hypodermic syringe assembly in which a syringe barrel is disposed within an outside support which extends beyond a needle attached to the syringe. Extending from the support is a canister that is filled with a thermal energy storage solution. The support surrounds the hypodermic needle and extends beyond the needle, toward the patient's skin. A hole in the support allows the hypodermic needle to contact the patient's skin when the hypodermic needle and syringe barrel are slidably advanced along the support. Prior to use, the syringe and canister assembly are put in a freezer at a temperature as low as 0 degrees Fahrenheit for approximately an hour. After removal from the freezer, the syringe assembly is effective for use for a minimum of three minutes during which time the canister is pressed against the skin where injection is to occur and is held against the skin for a time period ranging between ten to thirty seconds. In addition to requiring external freezer apparatus, the syringe arrangement is effective only for a relatively short time, requiring that the injection be given in close proximity to the freezing apparatus.
U.S. Pat. No. 3,605,742—Tibbs provides a relatively massive mechanism for operating a hypodermic syringe. Included is a plunger operating mechanism including a spring-loaded piston. A container of pressurized, highly volatile cooling liquid such as a fluorinated or chlorinated hydrocarbon, is mounted along side the mechanism which holds and operates the syringe. The pressurized coolant is released adjacent the hypodermic needle so as to surround the needle tip while contacting the patient's skin. The mechanism increases the size and weight of the syringe at least several times over, and renders the combination unsuitable for many applications where pressurized gas is not available and/or a bulky hypodermic injecting device is unsuitable.
U.S. Pat. No. 5,578,014—Erez et al. also discloses a relatively massive, bulky hypodermic injecting arrangement. Included is a holder for a hypodermic syringe joined to an adjacent forced air cooling system in which a fan cools a heat sink attached to a cooling plate. The cooling plate is located between the hypodermic needle and the patient's skin and includes a central passageway allowing the hypodermic needle to contact the patient's skin. The syringe is mounted for movement along a guide rod which orients the hypodermic needle with the central passageway of the cooling plate. The cooling plate first contacts the patient's skin and after a sufficient time has elapsed, the hypodermic syringe is advanced through a hole in the cooling plate, bringing the hypodermic needle in contact with the patient's skin. The entire mechanism increases the size and mass of the hypodermic syringe several times, rendering the device unsuitable where a portable, light weight hypodermic injection system is required.
U.S. Patent Application No. 2005/0182364 A1 discloses a cooling device utilizing ice as the cooling source. The device is provided for relieving pain associated with hypodermic injections, with the device being separate from the hypodermic syringe. A quantity of water is disposed within a hollow body that includes a retaining rod disposed within the water, and a removable cover for containing the water in contact with the retaining rod. Upon freezing, the water is converted to ice that adheres to the retaining rod, allowing the cover to be removed, thereby exposing the ice for contact to the patient's skin. After use, the device is discarded. Thus, external freezing apparatus is required to convert the water to a solid piece of ice, rendering the device unsuitable for applications where freezing apparatus is not available.